[1] I think the problem with the idea of the "Frontier" is that buys into USAmerican ideas of Westward Expansion and Manifest Destiny--and the problem with THAT is there wasn't really a frontier for the people who already lived there at the time. Oof. But it's so embedded into SF tropes ...
[2] ... and the language often seems inescapable. ("Space! The Final Frontier!" or even the idea of the "Undersea Frontier") There was, only within the last couple of days, a huge blowup online because a big SF con called the hotel The Frontier and guests "Pioneers."
I can see what you mean: it can seem pregnant with problematic histories. Having said that, Frontier can also mean outermost, outward, the edge of something.
Known Space Stellar Worlds I think there's a scout society mentioned somewhere. Altho in the KH modules the PCs are explicitly part of the UFO (or are by the end)
I expect 'Known Space' might ring some bells in Larry Niven Land.
Upf not UFO, thanks autocorrect
That's where my suggestion came from. UPF is such a through line.